There has been proposed a constant-speed control apparatus for a car which adjusts the degree of opening of a throttle valve by a driving stroke of a motor-driven actuator to run the car at a predetermined car speed.
FIG. 9 is a diagram showing a conventional constant-speed cruising apparatus. In FIG. 9, a motor-driven type actuator 20 is driven by a driving motor 21 to turn a lever 25 firmly attached to an output shaft 23 to thereby move a transmitting wire 26 connected to the end of the lever 25. A throttle valve 31 is placed in a carburetor 30 and is provided with links 32a and 32b. A wire 34 connects an end of the link 32b to an accelerating pedal 33. A reference numeral 35 designates the engine of a car, a numeral 36 designates a speed meter which detects a car speed by a car sensor to display the speed, a numeral 37 designates a control unit which compares an actual car speed detected by the car sensor with a car speed previously set and supplies to the motor-driven type actuator 20 a control signal on the basis of the comparison, and a numeral 38 designates a switch panel provided with a group of switches for setting or lowering the car speed.
FIG. 10 shows the construction of the actuator 20 in detail. In FIG. 10, a reference numeral 22 designates external lead wires drawn from a housing 20a. The driving motor 21 is mounted on the housing 20a to turn the output shaft 23 extending from the housing 20a in the range of an angle of swing .theta.. Namely, the actuator 20 drives the transmitting wire 26 within the angle of swing .theta. to open and close the throttle valve 31 under controlled condition, wherein the moving speed (gain) of the transmitting wire 26 is constant in the entire region of the angle of swing .theta.. Thus, in the conventional constant-speed cruising apparatus, the characteristic of a predetermined car speed to a opening/closing speed of the throttle valve (hereinbelow referred to as a gain characteristic) is substantially flat.
However, there have been various demands in the gain characteristics depending on the kind of car. For instance, a high responsiveness is required for the constant-speed cruising apparatus to be mounted on a sports car, since there is some allowability in driving function and accelerating speed on the sports can in comparison with commercial cars or passengers cars. Accordingly, the gain characteristic having linearity with respect to the predetermined car speed is required.
For the commercial cars which are generally used for carrying a relatively large load, it is unnecessary to have a high responsiveness as required in the sports cars, and the gain characteristic of a flat shape in the entire region of the predetermined car speed is required.
For the passenger cars, there is such a demand that a linear gain characteristic like that of a sports car is required in the middle speed region, and a saturation or descending characteristic is required in a high speed region from the viewpoint of stability in car cruising operations.
Thus, the conventional constant-speed cruising apparatus having the substantially flat, constant gain characteristic could not satisfy such requirements in correspondence to various kinds of cars.